U.S. patent application number 16/134946 was filed with the patent office on 2019-04-25 for ultra-small-sized 4k-resolution ultra-short-focus projection optical system.
The applicant listed for this patent is UNION OPTECH CO., LTD.. Invention is credited to Junqiang Gong.
Application Number | 20190121093 16/134946 |
Document ID | / |
Family ID | 61098536 |
Filed Date | 2019-04-25 |
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United States Patent
Application |
20190121093 |
Kind Code |
A1 |
Gong; Junqiang |
April 25, 2019 |
Ultra-Small-Sized 4K-Resolution Ultra-Short-Focus Projection
Optical System
Abstract
The present invention discloses an ultra-small-sized
4K-resolution ultra-short-focus projection optical system, which is
characterized by including in sequence in a projection direction: a
DMD chip, an equivalent prism, a 4K oscillating mirror, a
refraction lens assembly and an aspherical reflector. Through
reasonable distribution of focal power, the semi-aperture size of
the reflector is reduced to be less than 50 mm, and the assembling
sensitivity is substantially reduced, so that batch production can
be realized.
Inventors: |
Gong; Junqiang; (Zhongshan,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UNION OPTECH CO., LTD. |
Zhongshan |
|
CN |
|
|
Family ID: |
61098536 |
Appl. No.: |
16/134946 |
Filed: |
September 18, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 13/0045 20130101;
G03B 21/008 20130101; G02B 13/0065 20130101; G02B 17/08 20130101;
G03B 21/28 20130101; G02B 13/16 20130101; G03B 21/142 20130101;
G03B 21/147 20130101; G02B 17/0852 20130101 |
International
Class: |
G02B 13/00 20060101
G02B013/00; G03B 21/14 20060101 G03B021/14; G03B 21/00 20060101
G03B021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2017 |
CN |
201710990235.3 |
Claims
1. An ultra-small-sized 4K-resolution ultra-short-focus projection
optical system, characterized by comprising in sequence in a
projection direction: a DMD chip, an equivalent prism, a 4K
oscillating mirror, a refraction lens assembly and an aspherical
reflector, wherein the refraction lens assembly comprises in
sequence along the projection direction: a first lens group capable
of moving back and forth relative to the DMD chip, a second lens
group capable of moving back and forth relative to the DMD chip and
a third lens group which is static relative to the DMD chip; the
first lens group has positive focal power; the second lens group
has positive focal power; and the third lens group has negative
focal power.
2. The ultra-small-sized 4K-resolution ultra-short-focus projection
optical system according to claim 1, characterized in that the
first lens group comprises a first lens, a second lens, a third
lens, a fourth lens, a fifth lens, a sixth lens, a diaphragm and a
seventh lens in sequence along the projection direction; the second
lens group comprises an eighth lens, both surfaces of which are
bent towards the DMD chip; the third lens group comprises a ninth
lens, a tenth lens and an eleventh lens in sequence along the
projection direction; the first lens has positive focal power; the
second lens has negative focal power; the third lens has positive
focal power; the fourth lens has negative focal power; the fifth
lens has positive focal power; the sixth lens has negative focal
power; the seventh lens has positive focal power; the eighth lens
has positive focal power; the ninth lens has positive focal power;
the tenth lens has negative focal power; and the eleventh lens has
negative focal power.
3. The ultra-small-sized 4K-resolution ultra-short-focus projection
optical system according to claim 1, characterized in that the DMD
chip is deviated relative to an optical axis, and has a size of
0.48 inch and a resolution of 1920*1080.
4. The ultra-small-sized 4K-resolution ultra-short-focus projection
optical system according to claim 2, characterized in that the
focal power of the first lens group satisfies
0.04.ltoreq.|.phi..sub.410|.ltoreq.0.05; the focal power of the
second lens group satisfies
0.0002.ltoreq.|.phi..sub.420|.ltoreq.0.0003; the focal power of the
third lens group satisfies
0.009.ltoreq.|.phi..sub.430|.ltoreq.0.0092; and the focal power of
the aspherical reflector satisfies
0.05.ltoreq.|.phi..sub.500|.ltoreq.0.06.
5. The ultra-small-sized 4K-resolution ultra-short-focus projection
optical system according to claim 4, which is characterized in that
the third lens group is a glass aspherical lens; and the third lens
group is made of low-dispersion glass, which satisfies
70<Vd.sub.420<95.
6. The ultra-small-sized 4K-resolution ultra-short-focus projection
optical system according to claim 2, characterized in that both
surfaces of the eleventh lens are back on to the DMD chip; the
focal power of the eleventh lens satisfies
0.016.ltoreq.|.phi..sub.11|.ltoreq.0.018; and a distance between
the eleventh lens and the diaphragm is longer than 62 mm.
7. The ultra-small-sized 4K-resolution ultra-short-focus projection
optical system according to claim 6, characterized in that the
eleventh lens is a plastic aspherical lens; a first surface of the
tenth lens is bent towards the DMD chip, and a second surface of
the tenth lens is back on to the DMD chip; the focal power
satisfies 0.02.ltoreq.|.phi..sub.10|.ltoreq.0.021; and the ninth
lens is a bi-convex lens, and has the focal power satisfying
0.021.ltoreq.|.phi..sub.9|.ltoreq.0.022.
8. The ultra-small-sized 4K-resolution ultra-short-focus projection
optical system according to claim 2, characterized in that the
sixth lens is a glass aspherical lens, and has the focal power
satisfying 0.042.ltoreq.|.phi..sub.6|.ltoreq.0.043.
9. The ultra-small-sized 4K-resolution ultra-short-focus projection
optical system according to claim 2, characterized in that the
fourth lens and the fifth lens are glued lenses; glued surfaces are
back on to the DMD chip, and the focal powers are negative and
satisfy 0.005.ltoreq.|.phi..sub.45|.ltoreq.0.006; the second lens
and the third lens are glued lenses; glued surfaces of the second
lens and the third lens are back on to the DMD chip; and the focal
powers are positive and satisfy
0.022.ltoreq.|.phi..sub.23|.ltoreq.0.023.
10. The ultra-small-sized 4K-resolution ultra-short-focus
projection optical system according to claim 2, characterized in
that the first lens is a glass aspherical surface, and has the
focal power .phi..sub.1 satisfying
0.034.ltoreq.|.phi..sub.1|.ltoreq.0.036.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of Chinese Patent
Application No. 201710990235.3 filed on Oct. 23, 2017. All the
above are hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to a projection optical
system, and more particularly relates to an ultra-small-sized
4K-resolution ultra-short-focus projection optical system.
BACKGROUND ART
[0003] In recent years, with the development of projection
technologies, projectors have been widely used in home, education,
office and other fields, among which ultra-short-focus projection
has been widely used in home, office and other fields due to its
characteristic of projection of a large picture within a short
distance.
[0004] At present, ultra-short-focus projection lenses, the sizes
of which are limited by projection ratios, in the market are mainly
designed as structures of refraction lens groups and reflection
lens groups. Most of the ultra-short-focus projection lenses in the
market have overall lengths more than 250 mm. Although the overall
lengths of some ultra-short-focus projection lenses can be made
below 250 mm, the projection ratios are sacrificed and a relatively
small overall length and a relatively large projection ratio cannot
be realized at the same time. A DMD chip in the market at present
only supports the 1080P resolution. To support the 4K resolution,
it needs to add an oscillating mirror between a lens and a lighting
chip to convert 1 pixel into 4 pixels through a periodic vibration
mode of the oscillating mirror to achieve the 4K resolution, so
that a space for the oscillating mirror is required to be reserved
in the back focal length of the lens, which would substantially
increase the back focal length of the lens at this time, and the
resolution and the projection ratio have to be sacrificed in order
to realize a relatively short overall length. There is no
ultra-short-focus lens capable of overcoming the above-mentioned
disadvantages at the same time in the market at present.
[0005] The present invention is designed on the basis of such
case.
SUMMARY OF THE INVENTION
[0006] The present invention aims to overcome the defects in the
prior art and provide an ultra-small-sized 4K-resolution
ultra-short-focus projection optical system having a projection
ratio less than 0.21 and an overall optical length less than 202
mm.
[0007] Compared with the prior art, the present invention has the
following advantages:
[0008] 1. The ultra-small-sized 4K-resolution ultra-short-focus
projection optical system is extremely high in resolution
(supporting the 4K resolution), realizes the projection ratio less
than 0.21, and does not cause a suppositional focus in a
high-temperature state.
[0009] 2. Through reasonable distribution of focal power in the
ultra-small-sized 4K-resolution ultra-short-focus projection
optical system, the semi-aperture size of a reflector is reduced to
be less than 50 mm, and the assembling sensitivity is substantially
reduced, so that batch production can be realized.
[0010] 3. The ultra-small-sized 4K-resolution ultra-short-focus
projection optical system can compensate conjugate distance
variations under different projection distances and also correct
field curvatures and distortions under different projection
distances, so as to keep the resolutions under different projection
distances unchanged.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic diagram of the present invention.
[0012] FIG. 2 is a schematic diagram of a light path of the present
invention, in which a thin line is the light path.
[0013] In the drawings: 100: DMD chip; 200: equivalent prism; 300:
4K oscillating mirror; 410: first lens group; 420: second lens
group; 430: third lens group; 500: aspherical reflector; 1: first
lens; 2: second lens; 3: third lens; 4: fourth lens; 5: fifth lens;
6: sixth lens; 7: seventh lens; 8: eighth lens; 9: ninth lens; 10:
tenth lens; 11: eleventh lens; and 12: diaphragm.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Technical features of the present invention are further
described below in detail in combination with accompanying drawings
to facilitate understandings of those skilled in the art.
[0015] Referring to FIGS. 1-2, an ultra-small-sized 4K-resolution
ultra-short-focus projection optical system includes in sequence
along a projection direction: a DMD chip 100, an equivalent prism
200, a 4K oscillating mirror 300, a refraction lens assembly and an
aspherical reflector 500.
[0016] The refraction lens assembly includes in sequence along the
projection direction:
[0017] a first lens group 410 capable of moving back and forth
relative to the DMD chip 100, wherein the focal power of the first
lens group 410 is positive and the first lens group is capable of
moving back and forth relative to the DMD chip to compensate a
variation of a back focal length during lens assembling;
[0018] a second lens group 420 which is capable of moving back and
forth relative to the DMD chip 100, wherein the focal power of the
second lens group 420 is positive; and
[0019] a third lens group 430 which is static relative to the DMD
chip 100, wherein the focal power of the third lens group 430 is
negative.
[0020] According to the above ultra-small-sized 4K-resolution
ultra-short-focus projection optical system, the first lens group
410 includes a first lens 1, a second lens 2, a third lens 3, a
fourth lens 4, a fifth lens 5, a sixth lens 6, a diaphragm 12 and a
seventh lens 7 in sequence along the projection direction. The
second lens group 420 includes an eighth lens 8, both surfaces of
which are bent towards the DMD chip 100. The third lens group 430
includes a ninth lens 9, a tenth lens 10 and an eleventh lens 11 in
sequence along the projection direction.
[0021] Further, the first lens 1 has positive focal power. The
second lens 2 has negative focal power. The third lens 3 has
positive focal power. The fourth lens 4 has negative focal power.
The fifth lens 5 has positive focal power. The sixth lens 6 has
negative focal power. The seventh lens 7 has positive focal power.
The eighth lens 8 has positive focal power. The ninth lens 9 has
positive focal power. The tenth lens 10 has negative focal power.
The eleventh lens 11 has negative focal power.
[0022] According to the above ultra-small-sized 4K-resolution
ultra-short-focus projection optical system, the DMD chip 100 is
deviated relative to the optical axis, so that the center of the
DMD chip 100 has a deviation amount more than 125% relative to the
optical axis to ensure that an emergent light ray of the refraction
lens group does not interfere with the refraction lens group after
passing through the aspherical reflector. The DMD chip has 0.48
inch, and has the resolution of 1920*1080 and supports a 0.5-inch
ECD chip.
[0023] An image light beam is emitted from the DMD chip 100 and
then passes through the equivalent prism 200 and the 4K oscillating
mirror 300. When the 4K oscillating mirror 300 vibrates
periodically, a signal sent by the DMD chip 100 may be extended by
4 times to output 4K resolution. When the 4K oscillating mirror
does not vibrate, the output signal is 1 time at the resolution of
1080P. The refraction lens assembly receives the light ray
outputted by the 4K oscillating mirror, and primary imaging is
realized between the refraction lens assembly and the aspherical
reflector 500. The aspherical reflector 500 reflects a primary
image to a projection screen to form a high-resolution image.
[0024] According to the above ultra-small-sized 4K-resolution
ultra-short-focus projection optical system, the focal power of the
first lens group 410 satisfies
0.04.ltoreq.|.phi..sub.410|.ltoreq.0.05. The focal power of the
second lens group 420 satisfies
0.0002.ltoreq.|.phi..sub.420|.ltoreq.0.0003. The focal power of the
third lens group 430 satisfies
0.009.ltoreq.|.phi..sub.430|.ltoreq.0.0092. The focal power of the
aspherical reflector 500 satisfies
0.05.ltoreq.|.phi..sub.500|.ltoreq.0.06. When the lens groups are
distributed according to the above-mentioned focal powers, a
projection ratio less than 0.21 may be achieved, and the overall
length of the optical system is less than 202 mm. The 4K
oscillating mirror can be assembled between the optical system and
the DMD chip, and the semi-aperture size of the aspherical
reflector 500 also can be less than 50 mm. In addition, the
sensitivity of a fitting allowance of the system can be
substantially reduced, and batch production can be realized.
[0025] According to the above ultra-small-sized 4K-resolution
ultra-short-focus projection optical system, the focal power of the
second lens group 420 is positive and satisfies
0.0002.ltoreq.|.phi..sub.420|.ltoreq.0.0003. The third lens group
420 is a glass aspherical surface, and both surfaces of the third
lens group 420 are bent towards the DMD chip 100. The third lens
group 420 is made of low-dispersion glass and satisfies
70<Vd.sub.420<95. Conjugate distance variations under
different projection distances can be compensated after the above
conditions are satisfied simultaneously. Meanwhile, field
curvatures and distortions under different projection distances
also can be corrected, so as to keep the resolutions under
different projection distances unchanged.
[0026] According to the above ultra-small-sized 4K-resolution
ultra-short-focus projection optical system, the focal power of the
eleventh lens 11 is negative. Both surfaces of the eleventh lens 11
are back on to the DMD chip 100. The focal power of the eleventh
lens 11 satisfies 0.016.ltoreq.|.phi..sub.11|.ltoreq.0.018. A
distanced between the eleventh lens 11 and the diaphragm 12 is
longer than 62 mm. The eleventh lens 11 can be kept at a
temperature below 30.degree. C. during use of the lens, which
ensures that an optical focus does not drift when the projection
system outputs luminance over 4000 lumens, so that a picture of the
lens is still clear during long-time use of a projector without
being focused.
[0027] According to the above ultra-small-sized 4K-resolution
ultra-short-focus projection optical system, the second lens 2 and
the third lens 3 are adhered through optical glue, and the fourth
lens 4 and the fifth lens 5 are adhered through the optical
glue.
[0028] According to the above ultra-small-sized 4K-resolution
ultra-short-focus projection optical system, the first lens 1, the
sixth lens 6 and the eighth lens 8 are glass aspherical surfaces,
and the eleventh lens 11 and the aspherical reflector 300 are
plastic aspherical lenses.
[0029] The eleventh lens 11 has the negative focal power and is a
plastic aspherical lens, so as to correct coma aberrations and
distortions which are generated by a large visual field.
[0030] The tenth lens 10 has the negative focal power; the first
surface is bent towards the DMD chip and the second surface is back
on to the DMD chip; and the ninth lens 9 has the positive focal
power and is a bi-convex lens, and the focal powers satisfy
0.016.ltoreq.|.phi..sub.11|.ltoreq.0.018,
0.02.ltoreq.|.phi..sub.10|.ltoreq.0.021 and
0.021.ltoreq.|.phi..sub.9|.ltoreq.0.022, so that high-grade
astigmatisms and distortions of a large visual field can be
corrected, and furthermore, the height of a light ray entering a
rear group is reduced, the sensitivity of the tolerance of the
system is reduced, and a relatively large projection ratio is
realized.
[0031] The sixth lens 6 is a glass aspherical lens and has the
negative focal power. The focal power .phi..sub.6 satisfies
0.042.ltoreq.|.phi..sub.6|.ltoreq.0.043. The sixth lens 6 can
correct diaphragm spherical aberrations and diaphragm coma
aberrations, so that the system can support an aperture of 2.2 at
most.
[0032] The fourth lens 4 and the fifth lens 5 are glued lenses; the
glued surfaces are back on to the DMD chip; and the focal powers
are negative and satisfy 0.005.ltoreq.|.phi..sub.45|.ltoreq.0.006.
The second lens 2 and the third lens 3 are glued lenses; the glued
surfaces are back on to the DMD chip; and the focal powers are
positive and satisfy 0.022.ltoreq.|.phi..sub.23|.ltoreq.0.023, so
that vertical axis chromatic aberrations of a large visual field
and axial chromatic aberrations under different wavelengths can be
corrected, and an optical system has good color reduction
performance.
[0033] The first lens 1 is glass aspherical lens and has the
positive focal power. The focal power .phi..sub.1 satisfies
0.034.ltoreq.|.phi..sub.1|.ltoreq.0.036. The first lens 1 can
correct high-grade astigmatisms of a large visual field, and the
system can obtain relatively high resolution.
[0034] Further, shapes of the aspherical surfaces of the aspherical
reflector 500, the eleventh lens 11, the eighth lens 8, the sixth
lens 6 and the first lens 1 satisfy the following equation:
Z=cy.sup.2/{1 {square root over
(1-(1+k)c.sup.2y.sup.2)}}+a.sub.1y.sup.2+a.sub.2y.sup.4+a.sup.3y.sup.6+a.-
sub.4y.sup.8+a.sub.5y.sup.10+a.sub.6y.sup.12+a.sub.7y.sup.14+a.sub.8y.sup.-
16.
[0035] In this formula, parameter c is a curvature corresponding to
the radius; y is a radial coordinate, the unit of which is the same
as the length unit of the lens; and k is a conical quadratic curve
coefficient. When k coefficient is less than -1, the surface shape
curve of the lens is a hyperbolic curve. When k coefficient is
equal to -1, the surface shape curve of the lens is a parabola.
When k coefficient is between -1 and 0, the surface shape curve of
the lens is elliptical. When k coefficient is equal to 0, the
surface shape curve of the lens is circular. When k coefficient is
more than 0, the surface shape curve of the lens is flatly
circular. The parameters from a.sub.1 to a.sub.8 respectively
represent coefficients corresponding to all radial coordinates.
[0036] Actual design parameters of an ultra-short-focus lens which
has an optical overall length of 202 mm, a projection ratio of 0.21
and an aperture of 2.2, can support the 4K resolution and is
applicable to a 0.48-inch DMD chip are shown in the following
case:
TABLE-US-00001 Surface Thick- Optical number Type Radius R ness
material Aperture OBJ Object Infinity 420 3400 surface S1
Aspherical -33.9244 -84.98 MIRROR 98 surface S2 Aspherical 24.93938
-4.07 F52R 43 surface S3 Aspherical 123.8375 -12.04 46 surface S4
Standard 113.3287 -2.13 FDS1 39 S5 Standard -77.83142 -1.46 39 S6
Standard -160.6655 -9.15 H-LAK10 39 S7 Standard 36.21149 -2.0 39 S8
Aspherical -377.2177 -6.53 M-FCD1 33 surface S9 Aspherical -461.567
-16.82 29 surface S10 Standard -18.87146 -3.5 H-ZF52A 17 S11
Standard 4196.881 -4.75 15 STO Diaphragm Infinity 0.92 6.7 S13
Aspherical 21.8358 -3.55 M-TAFD305 7.14 surface S14 Aspherical
-259.508 -0.69 8.9 surface S15 Standard 19.18571 -5.21 FCD1 9 S16
Standard 5.698087 -2.96 TAFD55 10.6 S17 Standard 10.8387 -0.1 15.4
S18 Standard -40.55309 -8.48 FCD1 19.4 S19 Standard 13.22023 -2.61
TAFD25 20.4 S20 Standard 21.6251 -0.1 23.5 S21 Aspherical -116.4632
-6.85 M-FCD1 25.5 surface S22 Aspherical 15.91648 -0.1 25 surface
S23 Standard infinity -2 H-K9L 24 S24 Standard infinity -1.5 24 S25
Standard infinity -15 H-LAK52 21 S26 Standard infinity -6.9 21 IMA
Image infinity 18.5 surface
[0037] Coefficients of the aspherical reflector S1 are as
follows:
[0038] k: -1.800739
[0039] a.sub.1: 0
[0040] a.sub.2: -1.0597327e-006
[0041] a.sub.3: -8.3222807e-011
[0042] a.sub.4: 2.3262252e-014
[0043] a.sub.5: -5.4686126e-018
[0044] a.sub.6: -2.5680055e-022
[0045] a.sub.7: -1.1154829e-025
[0046] a.sub.7: 2.0543698e-030
[0047] Coefficients of the first surface S2 of the eleventh lens 11
are as follows:
[0048] k: -3.723038
[0049] a.sub.1: 0
[0050] a.sub.2: 7.4215285e-006
[0051] a.sub.3: 9.4657756e-009
[0052] a.sub.4: 7.0844328e-013
[0053] a.sub.5: -5.5787244e-015
[0054] a.sub.6: 5.4775315e-019
[0055] a.sub.7: 2.2404819e-021
[0056] Coefficients of the second surface S3 of the eleventh lens
11 are as follows:
[0057] k: 10.12091
[0058] a.sub.1: 0
[0059] a.sub.2: 1.7333935e-005
[0060] a.sub.3: -5.9351042e-009
[0061] a.sub.4: 5.6982012e-015
[0062] a.sub.5: -2.9748251e-018
[0063] a.sub.6: -7.0619502e-023
[0064] Coefficients of the first surface S8 of the eighth lens 8
are as follows:
[0065] k: 379.1852
[0066] a.sub.1: 0
[0067] a.sub.2: -2.4030546e-005
[0068] a.sub.3: 2.5671249e-008
[0069] a.sub.4: -8.0809034e-012
[0070] a.sub.5: 6.2264618e-014
[0071] a.sub.6: -2.2279804e-018
[0072] a.sub.7: -1.813092e-020
[0073] Coefficients of the second surface S9 of the eighth lens 8
are as follows:
[0074] k: 800
[0075] a.sub.1: 0
[0076] a.sub.2: -2.7050739e-005
[0077] a.sub.3: 8.9989552e-009
[0078] a.sub.4: 9.6252377e-011
[0079] a.sub.5: -1.0058039e-013
[0080] a.sub.6: 3.065522e-016
[0081] a.sub.7: 3.2106932e-019
[0082] Coefficients of the first surface S13 of the sixth lens 6
are as follows:
[0083] k: -16.86757
[0084] a.sub.1: 0
[0085] a.sub.2: -3.0493001e-005
[0086] a.sub.3: 4.0445005e-008
[0087] a.sub.4: -5.530555e-008
[0088] a.sub.5: 4.5462955e-009
[0089] a.sub.6: 3.0718419e-010
[0090] a.sub.7: 3.1582859e-011
[0091] a.sub.8: -3.9631704e-012
[0092] Coefficients of the second surface S14 of the sixth lens 6
are as follows:
[0093] k: -799.9997
[0094] a.sub.1: 0
[0095] a.sub.2: -0.0001689683
[0096] a.sub.3: 5.4774441e-006
[0097] a.sub.4: 3.0956184e-009
[0098] a.sub.5: 1.5690797e-009
[0099] a.sub.6: -9.1244185e-011
[0100] a.sub.7: 9.8724083e-012
[0101] a.sub.8: -2.5520602e-013
[0102] Coefficients of the first surface S21 of the first lens 1
are as follows:
[0103] k: 62.06816
[0104] a.sub.1: 0
[0105] a.sub.2: -2.0802011e-005
[0106] a.sub.3: -2.1441118e-007
[0107] a.sub.4: 6.4465877e-010
[0108] a.sub.5: -1.9932042e-012
[0109] a.sub.6: -6.0476728e-016
[0110] a.sub.7: 1.5282876e-018
[0111] a.sub.8: 5.03457e-021
[0112] Coefficients of the second surface S22 of the first lens 1
are as follows:
[0113] k: -1.830338
[0114] a.sub.1: 0
[0115] a.sub.2: -4.1501526e-005
[0116] a.sub.3: -1.6048089e-007
[0117] a.sub.4: 3.9708184e-012
[0118] a.sub.5: -1.0644763e-012
[0119] a.sub.6: 9.4283887e-016
[0120] a.sub.7: 1.9633741e-018
[0121] a.sub.8: 1.2561911e-020
[0122] An ultra-short-focus projection lens has a projection range
of 0.4 m to 0.6 m. During focusing of the ultra-short-focus
projection lens, the first lens group 410 is moved to adjust the
back focal length within +/-0.2 mm. After the back focal length is
adjusted, the first lens group 410 is fixed, and the second lens
group 420 is moved to realize focusing. During focusing, varying
ranges of gaps between the lens groups are as follows: a gap
between the first lens group 410 and the second lens group 420 is
2.2 to 0.4 mm, and a gap between the second lens group 420 and the
third lens group 430 is 16.62 to 18.42 mm.
[0123] The present invention is described above in detail in
combination with the drawings and embodiments. Those ordinary
skilled in the art can make various change examples to the present
invention according to the above-mentioned description. Therefore,
some details in the embodiments shall not constitute a limitation
to the present invention. The present invention will take the scope
defined by attached claims as the protection scope of the present
invention.
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